1. Field of the Invention
The present invention relates to a method of controlling a welding output and also relates to a consumable electrode type pulse arc welding device in which a consumable electrode, which will be referred to as a wire hereinafter, is automatically fed, and a peak current and a base current are alternately and repeatedly supplied between the wire and a welding base metal which will be referred to as a base metal hereinafter.
2. Description of the Related Art
FIG. 10 is a view showing an example of the conventional method of controlling an output of a consumable electrode type pulse arc welder. According to the above conventional method, an output of the pulse arc welder is controlled by fixing a pulse period and changing a pulse frequency. This pulse period is set at the most appropriate value so that a melting drop can be formed at a tip of a wire each time a peak current is outputted and the thus formed melting drop can be separated from the tip of the wire by an electromagnetic pinching force caused by the peak current and shifted to a base metal. Therefore, as shown in FIG. 11, under the outputting condition of one pulse and one drop, the occurrence of short circuit is suppressed and spattering is seldom caused during a process of welding.
Next, referring to FIG. 10, a structure of the conventional consumable electrode type pulse arc welding device will be explained below. In FIG. 10, reference numeral 1 is a three-phase input power source, reference numeral 2 is a first rectifying section, reference numeral 3 is an inverter circuit, reference numeral 4 is a main transformer, reference numeral 5 is a second rectifying section, reference numeral 6 is a reactor, reference numeral 20 is a positive output terminal, reference numeral 21 is a negative output terminal, reference numeral 22 is a chip, reference numeral 23 is a wire, and reference numeral 24 is a base metal. An error caused between an output of the welding voltage detecting section 7 and an output of the welding voltage setting section 9 is amplified by the error amplifying section 8. By an output of this error amplifying section 8, a pulse frequency signal is outputted by the pulse frequency calculating section 18. By this pulse frequency signal and an output of the pulse period setting section 13 for setting a pulse period, a frequency appropriate for a welding output and a signal corresponding to the pulse period are obtained in the pulse output setting section 10c.
When the most appropriate period for one pulse and one drop is set as described above, it is possible to suppress the occurrence of spattering. However, in recent years, there is a growing tendency of increasing a welding speed so that the productivity of welding can be enhanced. In order to increase the welding speed, it is necessary to lower a welding voltage. When the welding voltage is lowered, a pulse period is not changed according to the conventional controlling method as shown in FIG. 12. Therefore, an average of the pulse frequency is lowered. However, a quantity of a wire to be fed is constant. Accordingly, although the most appropriate period for one pulse and one drop has been set, short circuit occurs before a melting drop is separated from a wire tip because the pulse frequency lacks with respect to the quantity of wire to be fed. Further, a size of the melting drop which has been left at the tip of the wire is not uniform. Therefore, frequency of the occurrence of short circuit becomes irregular. For the above reasons, a quantity of generated spatter is increased, and the thus generated spatter adheres to the base metal and the nozzle, which impairs the enhancement of productivity.